A method of obtaining directivity in an optical waveguide includes the steps of falling incident light on surface of diffuse reflection members arranged at a center portion of the optical waveguide, generating a first table relative to an amount of emitted light that is acquired at a circumference of the optical waveguide by controlling at least one of an image control factor for changing an image of the incident light and a coordinate control factor for changing coordinates of the incident light with them being changed, and generating a second table relative to a pattern of the light which is incident to the diffuse reflection member by seeking for a combination of the image and the coordinates of the light based on the generated first table.